Plasma apparatuses are widely used in manufacturing semiconductor devices and flat panel displays, to perform processes such as oxide film formation, crystal growth of a semiconductor layer, etching and ashing. Among such plasma apparatuses, there is a high frequency plasma apparatus that supplies a high frequency electromagnetic field to a container using an antenna, and generates high frequency plasma using the electromagnetic field. The high frequency plasma apparatus is capable of generating plasma stably even when plasma gas pressure is relatively low, and hence, application thereof is wide.
FIG. 8 shows an exemplary configuration of a conventional high frequency plasma apparatus. This figure shows some parts in vertical cross section. FIGS. 9A and 9B are cross sections showing, in enlargement, the portion IX surrounded by dotted lines in FIG. 8.
As shown in FIG. 8, the plasma apparatus has a cylindrical processing container 511 with a bottom, opened at the upper portion. At the bottom of processing container 511, a mounting table 522 is fixed, and a substrate 521 is placed on an upper surface of mounting table 522. On a sidewall of processing container 511, a gas supply nozzle 517 is provided, and at the bottom of processing container 511, an exhaust port 516 is provided for vacuum evacuation. At the upper opening of processing container 511, a dielectric plate 513 is arranged, and at a joint portion between an upper surface of the sidewall of processing container 511 and a peripheral portion of a lower surface of dielectric plate 513, an O-ring 514 as a sealing member is interposed, to attain tight sealing of the joint portion.
On dielectric plate 513, a radial antenna 530 is arranged. At the central portion of radial antenna 513, a high frequency generator 545 generating a high frequency electromagnetic field is connected by a wave-guide. At the upper surface of the sidewall of processing container 511, an annular shield member 512 is arranged. Shield member 512 covers an outer periphery of dielectric plate 513 and radial antenna 530, so as to prevent leakage of the electromagnetic field to the outside of processing container 511.
Of the electromagnetic field emitted from radial antenna 530, an electromagnetic field F that has passed through dielectric plate 513 and introduced to processing container 511 causes electrolytic dissociation of a gas in processing container 511, to generate plasma in an upper space S2 above substrate 521. Here, an electromagnetic field F1 that is not absorbed by the plasma and reflected and an electromagnetic field F2 not directly introduced from radial antenna 530 to processing container 511 are repeatedly reflected in an area S1 between an emitting surface of radial antenna 530 and a plasma surface, forming a standing wave. The standing wave also takes a part in the generation of plasma.
In the conventional plasma apparatus, when shield member 512 is arranged at an upper surface of the sidewall of processing container 511, a distance L1 from an edge 511A of an inner surface of the sidewall of processing container 511 to an inner surface of shield member 512 is not at all considered. It is noted, however, that when wavelength of an electromagnetic field in a recessed portion 518 (dotted area in FIGS. 9A and 9B) formed by the upper surface of the sidewall of processing container 511, the emitting surface of radial antenna 530 and the inner surface of shield member 512 is given as λg and the distance L1 is approximately λg/4 as shown in FIG. 9A, the voltage at the position of edge 511A becomes large, possibly resulting in an abnormal discharge, as the position of edge 511A, that is the opening of recessed portion 518, corresponds to the bulged portion of the standing wave. If such an abnormal discharge occurs, metal atoms of processing container 511 may be dissociated, causing contamination in processing container 511.
In the conventional plasma apparatus, a distance L2 from the inner surface of shield member 512 to the position where O-ring 514 is arranged is not at all considered, either. When the distance L2 is approximately λg/4, elasticity of O-ring 514 degrades because of the strong electromagnetic field of the standing wave, and the life of O-ring 514 becomes shorter.